Many alternative support beams, mine props or mine pillars have been designed to replace the wooden support beam or reinforce the wooden support beam, but usually the high cost prevents it from entering the market. U.S. Pat. No. 4,712,947 disclose a timber load support member and a sleeve surrounding the support member in its axial direction. The timber prop had an initial length of 1200 mm with the surrounding sleeve made from mild steel being 900 mm long with a wall thickness of 2.8 mm. The timber fibres of the prop began to progressively separate in the direction transverse to the prop axis at around 30 mm and was fully load supporting at around 280 mm after a 23% reduction in length and around 60 tons of load. Quite a large displacement of wood or un-controlled yielding is seen over the length of the prop weakening the support beam with cracked fibres that can be seen at the head and foot part of the prop being held together by the relative expensive, heavy steel sleeve.
U.S. Pat. No. 6,910,834 disclose a mine support prop comprised of an outer steel shell formed in the shape of an elongate tube. An aerated or other lightweight concrete or cement is poured into the elongate tube to substantially fill the entire length of the tube. The total weight of the prop is 58 kg, has a length of 2 m, width of 150 mm and the sleeve diameter is 2 mm. A plurality of elongate steel support members having a length less than the elongate tube are attached to the tube to prevent buckling of the elongate tube along the portion of the tube to which the support members are attached. Buckling is more prone to happen with a relative high (>10) slenderness ratio (height to width ratio) when an elongate tube is exposed to sufficient axial force and therefore the use of the steel support members in the above specification. The elongate tube may be formed by fibreglass formation but no reference is made in the specification to its thickness, specific fibre orientation or that its required length may be less than the entire length of the tube. The mine prop can support a load above 22 tons until more than 175 mm of displacement have occurred. A high slenderness ratio prop is of benefit to the mines as they convey these props down the mine in the same “cart” as what they bring the ore to the surface and the higher the slenderness ratio the more props they can transport with the “cart” at any given time.
A need has thus been identified for a mine roof support overcoming at least some of the shortcomings of the above mine supports.